William has taken 3 exams and his average score so far is 85. If he gets 100, a perfect score, on the remaining 2 exams, what will his new average be?
If he gets 100 on the remaining exams, the sum of his scores will be $3 \cdot 85 + 2 \cdot 100 = 455$ His overall average will then be $455 \div 5 = 91$.